1. Field of the Invention
The present invention relates to a seal assembly used for sealing an annular cavity formed between the inner and outer rings of a bearing assembly, and interposed between the inner and outer rings of a bearing assembly, and more particularly to a seal assembly having an annular seal member and an annular seal lip extending from the annular seal member and being in elastic-contact with the sidewall of an annular groove formed in the outer peripheral surface of the inner ring.
2. Description of the Related Art
With reference to FIG. 9, there is provided an idler bearing assembly 1, used in an engine for automobiles or the like, has a non-rotatable bearing ring or inner ring 2 in the form of a boss and a rotatable bearing ring or outer ring 4 arranged coaxially with the inner ring 2 at the axial end portion of the outer peripheral surface of the inner ring 2. On the outer peripheral surface of the outer ring 4 is engaged a timing belt, not shown.
The idler bearing assembly 1 also has a plurality of bearing balls 6, a crown type retainer 8 for retaining rollingly these balls 6 between the inner and outer rings 2, 4 of the bearing assembly 1, a seal assembly 10 interposed between the inner and outer rings 2, 4 for sealing grease within the bearing assembly 1, and a bracket 12 fixed on the outer peripheral surface of the axial end portion of the inner ring 2.
Referring to FIG. 10, the bearing assembly 1 is fitted to a fixed section (not shown) by a bolt inserted into a through hole 13 of the bracket 12. In case of making a tension adjustment to the timing belt 15 engaged onto the outer peripheral surface of the outer ring 4, the bearing assembly 1 is rotated about the through hole 12 in the clockwise or counterclockwise direction indicated by arrows.
Through the above-mentioned movement of the bearing assembly 1, the tension of the timing belt 15 is adjusted. That is, as the timing belt 15 is pushed by the outer ring 4 with the clockwise rotation of the bearing assembly, the tension thereof increases. Conversely, the tension of the timing belt 15 decreases with the counterclockwise rotation of the bearing assembly.
After the tension of the timing belt 15 is thus adjusted, the bearing assembly 1 is fixed by means of a bolt 19 inserted into a long hole 17 formed in the inner ring 2, such that the timing belt 15 is held in an adjusted tension state.
With particular reference to FIG. 11, the conventional seal assembly 10 used in the above bearing assembly 1, has an annular seal member 14 extending radially between the inner and outer rings 2, 4 of the bearing assembly 1, and two radially extending bifurcated annular seal lips, that is, a first seal lip 16 and a second seal lips 18. The first seal lip 16 extends radially downwardly from the lower end portion of the seal member 14. The second seal lip 18 extends radially obliquely from the lower end portion of the seal member 14 so as to be in an axially opposed relation to the first seal lip 16. The seal member 14 comprises an annular metal plate 20 and an annular elastic body 22 such as rubber bonded on the peripheral surface of the plate 20 and is fixed onto the shoulder portion 24 formed on the inner peripheral surface of the outer ring 4. An annular groove 26 is continuously formed circumferentially in the outer peripheral surface of the inner ring 2. Each of the first and second lips 16, 18 confronts the inside of the annular groove 26 having a nearly perpendicular sidewall 28 and a radially outward tapered sidewall 30.
The first seal lip 16 is in elastic-contact with the sidewall 30 of the annular groove 26 at the lower end thick portion thereof, while the second seal lip 18 is in non-contact with and close to the sidewall 28 of the groove 26 of the inner ring 2.
With the above construction, the behavior of the first seal lip 16 not having a moderate rigidity corresponding to the contact with the sidewall 30 of the groove 26 will be explained hereinbelow.
That is, when the relative position between the inner and outer rings 2, 4 is varied due to vibration or shock on the bearing assembly 1, since the first and second seal lips 16, 18 are so constructed as to move together with the movement of the outer ring 4, the relative position between the lips 16, 18 and the annular groove 26 of the inner ring 2 is also varied.
Such a variation may cause the contact state of the first seal lip 16 and the sidewall 30 of the groove 26 to become loose, resulting in that the sealing condition for sealing the grease within the bearing assembly deteriorates and hence the grease becomes leaky from between the first seal lip 16 and the sidewall 30.
For instance, for the first seal lip 16 of a high rigidity, it is difficult to follow the relative movement of the inner and outer rings 2, 4 so that the contact area between the first seal lip 16 and the sidewall 30 of the annular groove 26 is not varied. On the other hand, for the first annular seal lip 16 of a low rigidity, it is easy to follow the relative movement. In this case, however, the function for intercepting grease within the seal assembly 10 deteriorates. Accordingly, the first seal lip 16 not having a moderate rigidity gives a high possibility of the grease leakage, especially in using the bearing assembly having a rotatable outer ring.
In the seal assembly 10 having the above construction, since the inside of the bearing assembly is nearly shut off the outside thereof with the first seal lip 16 in contact with the sidewall 30 of the annular groove 26, the internal pressure of the bearing assembly will increase with a rise in an internal temperature thereof and cause the first seal lip 16 to float off the sidewall 30 or excessively to come off the bearing assembly.
In order to suppress the increase in the internal pressure of the bearing assembly, communicating grooves capable of communicating axially between the inside and outside of the bearing assembly may be formed at the lower end thick portion of the inner ring 2. In the seal assembly 10 having such communicating grooves, however, the grease within the annular groove 26 becomes leaky outside the seal assembly 10 through the communicating grooves by means of the action of a centrifugal force developed by the bearing assembly rotating.